Improvements in aerials of the cosecantsquared type



L. THOUREL Jan. 23, 1962 IMPROVEMENTS IN AERIALS OF THE COSECANT-SQUARED TYPE Filed Dec. 1, 1959 United States Patent 9 3,018,480 IMPROVEMENTS IN AERIALS OF THE COSECANT- SQUARED TYPE Lo Thourel, Paris, France, assignor to Compagnie Generale de Telegraphic Sans Fil, a corporation of France Filed Dec. 1, 1959, Ser. No. 856,442 Claims priority, application France Dec. 19, 1958 5 Claims. (Cl. 343-771) The present invention relates to directional ultra high frequency aerials. More particularly, it relates to aerials whose radiating pattern is of the cosecant-squared type.

Aerials having this type of radiation pattern are currently associated with high coverage air field approach surveillance radars. However, in so far as airborne radars are concerned, the considerations tied to aerodynamics and to space requirements rapidly become of prime importance.

It is an object of the present invention to remedy the difiiculties which generally arise in this respect by providing a flat aerial, capable of being rapidly mounted in an aircraft for association with a radar system which may be, for example, aimed at exploring the underlying ground.

An aerial according to the invention comprises a waveguide, one of the large sides of which is slotted while the opposite side supports within the guide a dielectric body, the thickness of which changes at intervals.

The radiation pattern of the aerial is adjusted to the desired configuration by adjusting the thickness of the dielectric body, which may form a layer, and the width of the slots.

The invention will be best understood from the following description given by way of example, with reference to the appended drawing, in which:

FIG. 1 is a radiating pattern obtained with an aerial of the invention;

FIG. 2 shows a wave-guide with radiating slots of the known type;

FIG. 3 is an axial cross-sectional view of an aerial according to the invention.

As is well known, the general radiation pattern 11 of an aerial may be obtained by adding elementary patterns I, II, and III as shown in FIG. 1. The field radiated in any direction, such as for example the direction Ox, is given by the vector or and its magnitude is:

?, 66 and m5 being the respective radiation vectors corresponding to elementary diagrams I, II and III.

An aerial according to the invention comprises a slotted wave-guide 23, such as that shown in FIG. 2; the slots 21 are cut in one of the large walls 22 of guide 23. They are spaced apart from one another, for example by a quarter of a wavelength. When ultra high frequency energy is fed to the guide of FIG. 2 from one of its ends, for example end 24, it radiates in a direction 25 making an angle 0 with the plane of the slots.

As is well known, this angle is defined by the equation where X and A, are the lengths in the air and in the wave guide respectively of the operating wave.

3,018,4tiii Patented Jan. 23, 1962 According to the invention, wave guide 23 comprises a dielectric body. For example the bottom of wave guide 23 is covered with a layer of dielectric material 42, such as Teflon or a ceramic material, as shown in section in FIG. 3. The guide is thus divided in a plurality of waveguide sections, 47, 48 and 49, the thickness of the dielectric layer 43, 44 and 45 being different in each section and decreasing from the input end 41 of the guide to the opposite end. Energy is fed to the guide at the input end 41, the opposite end being coupled to a matched load 46. The described structure results in the wave length A varying from one guide section to the adjacent one, angle 0 varying accordingly and being smaller as the wavelength in the guide is greater, i.e. the dielectric layer thicker.

The system of FIG. 3 makes it possible to obtain a radiation pattern of the type shown in FIG. 1. By adjusting the respective amounts of dielectric material 43, 44 and 45, guide sections 47, 48 and 49 can be caused to radiate along the radiation patterns I, II and III respectively, the axes of these patterns being inclined to the upper surface of the guide by angle 0 0 and 0 respectively.

In addition, the radiating pattern can be further adjusted by providing guide sections 47, 48 and 49 with slots having different widths which may, for example, increase from one section to the other in the order named. As well known, the radiation coeflicient, by a slot having a given length, i.e. the ratio of the energy radiated by said slot to the energy propagating in the guide, is substantially proportional to the width of the slot, consequently, the width of the successive slots is a parameter for adjusting the radiation pattern.

It will be understood that the invention is not limited to the embodiment described which has been given only by way of example. Thus, a different number of wave guide sections could be used and the dielectric body need not form a continuous layer covering the bottom of the guide but may have any other shape or position.

What is claimed is:

1. An aerial comprising a wave-guide having two large and two small sides and two ends and including a plurality of guide portions of the same cross section, one of said large sides having equally spaced slots; and respective dielectric bodies having respective constant cross-sections in said guide portions, the volume of said bodies decreasing from one end of said guide to the other.

2. An aerial comprising a wave-guide having two large and two small sides and two ends including a plurality of guide portions of the same cross section, one of said large sides having equally spaced radiating slots; respective dielectric layers in said portions, said layers covering the other large side and the thickness of said layers decreasing from one end of said guide to the other.

3. An aerial comprising a wave-guide having two large and two small sides and two ends and including a plurality of guide portions of the same cross section, one of said large sides having equally spaced radiating slots; respective dielectric layers in said portions, said layers covering the other large side and the thickness of said layers decreasing from one end of said guide to the other and being constant in each of said guide portions.

4. An aerial comprising a wave-guide having two large and two small sides and two ends and including a plurality of guide portions of the same cross section; equally spaced radiating slots in one of the large sides; the width of said slots increasing from one end of said guide to the other; respective dielectric bodies in said portions, the volume of said bodies decreasing from said one end of said guide to said other end.

5. An aerial comprising a wave guide having two large and two small sides and two ends and including a plurality of guide portions, one of said large sides having equally spaced radiating slots; respective dielectric layers in said portions, said layers covering the other large side and the thickness of said layers decreasing from one end of said guide to the other and the width of said slots increasing from one end to said other end and being constant in each of said guide portions.

References Cited in the file of this patent UNITED STATES PATENTS 2,405,242 Southworth Aug. 6, 1946 2,433,368 Johnson et al Dec. 30, 1947 2,447,549 Willoughby Aug. 24, 1948 2,822,542 Butterfield Feb. 4, 1958 FOREIGN I PATENTS 902,510 Germany Jan. 25, 1954 1,014,722 France June 18, 1952 

